The invention concerns a sifting machine having a stationary sifting basket, a rotor rotating in the sifting basket and a worm conveyor feeding into an end of the sifting basket for dosing and introducing a material to be sifted, wherein the rotor and the worm conveyor are driven for rotation.
In sifting machines having a stationary sifting basket disposed within a sifting machine housing and having a rotor rotating therein, the material to be sifted is normally introduced by means of a worm conveyor which projects into an end of the sifting basket and transfers the material. The material is engaged by the rotor in the sifting basket and accelerated in a centrifugal fashion against the sifting surface of the sifting basket. The sifted material falls into a receiving hopper and is passed out of the sifting machine housing, whereas the course product is transported out at the end of the sifting basket facing away from the worm conveyor. This is generally effected in that the rotor plates have a slight tilt in the axial direction.
In order to drive the worm conveyor and the rotor for rotation, both seat on a common shaft and one single drive motor is provided for which is disposed on the end of the worm conveyor facing away from the rotor. The amount of material fed to the rotor depends on the rate of revolution of the drive motor and may not exceed certain values to prevent unsifted material from being removed along with the course material discharge. The rate of revolution must also be chosen in such a fashion that a sufficient dwell time in the sifting basket is guaranteed for the material being sifted. The highest degree of sifting efficiency for a sifting machine thereby requires, on the one hand, an optimal rotor rate of revolution for the actual sifting process and, on the other hand, an optimized rate of revolution for the worm conveyor with regard to the introduction of material. Since both rates of revolution are not equal and also depend on the material, it is always necessary to strike a compromise for operation of the drive motor with regard to the rate of revolution.
Attempts have been made to dispose an additional independently driven dosing device above the inlet chute of the worm conveyor so that the amount of material introduced to the sifting basket is no longer dependent on the rate of revolution of the worm conveyor so that the sifting machine can be operated with the optimized rate of rotor revolution. The additional dosing device is however associated with significant additional constructional effort and also requires extra clearance height in the vicinity of the inlet chute. This is undesirable, since it makes the filling process more difficult.
Another possibility for avoiding the above mentioned disadvantages is to provide the worm conveyor, at least in its dosing region, with a larger core diameter or with a steeper conveyor screw pitch for reducing the amount transported. If appropriate, the worm conveyor can also be exchanged for a worm conveyor having differing geometry. All these measures, however, constitute unacceptable compromises in practical applications.
When the material being sifted by the sifting machine is changed, the sifting machine must normally be cleaned. Towards this end, the worm conveyor, the sifting basket and the rotor must be removed. This is also true when exchanging the sifting basket for a differing grain spectrum. Removal and exchange is however difficult and costly due to the relatively large axial constructional extent.
It is therefore the underlying purpose of the invention to create a sifting machine of the above mentioned kind with which the rotor and the worm conveyor can be operated at optimized rates of revolution and which facilitates a simplified cleaning and reconfiguration.